1. Field of the Invention
The present invention relates to improvements in an auxiliary steering angle control system for a wheeled vehicle, and more particularly to an auxiliary steering angle control system which executes an auxiliary steering angle control with a feedback compensation.
2. Description of the Prior Art
Various auxiliary steering angle control systems for vehicles have been proposed and in practical use. Japanese Patent Provisional Publication No. 62-247979 discloses a typical auxiliary steering angle control system where an auxiliary steering control is executed by applying a feedback control and a feed-forward control to a vehicle motion variable.
However, such a conventional auxiliary steering angle control system is arranged to execute the feedback control during a vehicle running condition regardless of a road condition. Therefore, in case that the road condition is suddenly changed from a bad-conditioned surface such as a bumpy road to a good-conditioned surface, unexpected vehicle motion variable is occurred in the vehicle and impresses a strange feeling to a driver. That is, in case that the vehicle is traveling on an extremely bad-conditioned (bumpy) road, the tire contact area on a road surface is decreased. Accordingly, the cornering force of the tires is decreased and therefore the yaw rate generated by the steering operation becomes difficult to be change.